1. Field of the Invention
The present invention relates to a vane pump.
2. Description of the Related Art
As a vane pump, as described in WO2005/005837 (patent document 1), there is a structure having a rotor which is connected to a rotating shaft pivoted to an inner portion of a housing so as to rotate. A cam ring is arranged in such a manner as to surround the rotor in the inner portion of the housing. A plurality of vanes are slidably arranged in a plurality of vane grooves provided in a radial direction of the rotor. A plurality of pump chambers are defined by the adjacent vanes in the periphery of the rotor. A plurality of discharge ports corresponding to the pump chambers carrying out a compression stroke are provided to be opposed in a diametrical direction of the rotor. Notch grooves are extended in an inverse direction to a rotor rotation forward direction from hole edges in the inverse direction of the respective discharge ports. In this vane pump, a communication start point between each of the pump chambers and each of the discharge ports is quickened by the notch groove, and a communication time between the pump chamber and the discharge port becomes longer with respect to a rotating speed of the vane. Accordingly, since a moving time to the pump chamber of a working fluid pressure within the discharge port becomes longer, a hydraulic pressure change of the working fluid within the pump chamber becomes smaller. As a result, it is possible to reduce a serge pressure within the pump chamber and it is possible to lower an abnormal noise generation.
Further, as the vane pump, as described in Japanese Patent No. 3573242 (patent document 2), there is a structure in which a plurality of discharge ports are divided into a main discharge port which always carries out a discharge, and the other sub discharge port. For example, in the vane pump which is used in a power steering apparatus of a vehicle, it is desired to supply a sufficient flow rate to a fluid equipment of a steering in a low rotation area, and hold down an unnecessarily great flow rate for lowering uselessly consumed horse power in a high rotation area. Accordingly, in the low rotation area, a sufficient flow rate of pressure fluid is supplied to the fluid equipment from both of the main discharge port and the sub discharge port. Further, in the high rotation area, the pressure fluid is supplied to the fluid equipment only from the main discharge port, and the discharge oil of the sub discharge port is flowed back as surplus oil to a tank side (or an suction port corresponding to the same sub discharge port), thereby achieving a reduction of the consumed horse power.
FIGS. 7, 8A and 8B show the conventional vane pump mentioned above. Reference numeral 1 denotes a rotor. Reference symbol 1A denotes a vane groove. Reference symbol 1B denotes a vane. Reference symbol 1C denotes a pump chamber defined by the adjacent vanes 1B and 1B. Reference numeral 2 denotes a rotating shaft. Reference numeral 3 denotes a cam ring. Reference symbol 4M denotes a main discharge port. Reference symbol V1 denotes a notch groove. Reference symbol 4S denotes a sub discharge port. Reference symbol V2 denotes a notch groove, and reference numerals 5 and 6 denote a suction port. An extension length L1 of the notch groove V1 of the main discharge port 4M and an extension length L2 of the notch groove V2 of the sub discharge port 4S are set to the same length.
In the conventional vane pump mentioned above, in the case that the pressure fluid is supplied to the fluid equipment only from the main discharge port 4M, the working fluid pressure of the main discharge port 4M connected to a supply flow path to the fluid equipment becomes higher, and the working fluid pressure within the sub discharge port 4S connected to the tank side (or the suction port) becomes lower. As a result, as shown in FIG. 7, a relationship Fa>Fb is established between a pressure Fa which the working fluid pressure within the main discharge port 4M applies to the rotor 1 via the pump chamber 1C, and a pressure Fb which the working fluid pressure within the sub discharge port 4S applies to the rotor 1 via the pump chamber 1C, on a diameter of the rotor 1 which connects the main discharge port 4M and the sub discharge port 4S through the center of the rotor 1. The pressure difference Fa/Fb makes a center C of the rotor 1 displace from a center J of the cam ring 3 close to the sub discharge port 4S at a degree of a play of a serration by which the rotor 1 is connected to the rotating shaft 2 as shown in FIG. 8A to FIG. 8B. In accordance with this, the center C of the rotor 1 is offset from the center J of the cam ring 3, and in comparison with a timing at which the one vane 1B runs into the notch groove V1 of the main discharge port 4M, a timing at which the another vane 1B runs into the notch groove V2 of the sub discharge port 4S becomes faster, in two vanes 1B and 1B which are opposed to each other while holding the center C of the rotor 1 therebetween. Accordingly, the timings at which the respective pump chambers 1C defined by the vanes 1B are communicated respectively with the main discharge port 4M and the sub discharge port 4S are deviated from each other, and phases of pulsations of the hydraulic pressure within the respective discharge ports 4M and 4S are further deviated from each other, thereby causing an abnormal noise generation.